Tracking visitors on LJ is a bit of a tricky proposition. On most other websites, you are able to track number of visitors, where they come from, how long they spend there, which pages they look at, and even where in the world they are. If you had your blog hosted on your own server, you would be able to track all of these things easily.
But most people don't have their own servers. Most people don't host their blogs on their own servers. LiveJournal has its own servers, and doesn't offer tracking services, and probably won't, not ever. So how do you figure out who is reading your LJ?
There are a number of sites/services out there that offer at least the partial ability to view who is reading at least some of your LJ. They are often near-accurate, but there are some fundamental flaws with these services that people aren't always aware of.
Most, if not all, services like this rely on you putting a specific image or piece of code in your journal. It's usually an image, either a visible image of a size large enough to be seen, or an invisible image -- a 1x1 or other very small transparent image. More reputable sites may make their images visible rather than letting people think they might get away with surfing anonymously. Sometimes it's in the form of a counter; sometimes it's a little logo.
How does it work?
The image is remotely hosted: that is, it is stored on the tracking company's server. When someone loads your journal page, they also load the image from the tracking company's server. The tracking company's server pays attention to what IP addresses are loading the image, and then track stats.
They can tell what time the image was loaded, sometimes what page you came from, what page you went to, and by comparing those two, how long you spent on the site. If you know what IP address loaded an image, you can look up who owns that particular public IP address. Most IP addresses that people are going to be visiting you from are going to be owned by some form of internet service provider, and what location belonging to that particular ISP. You can tell whether the person is using Cox or Qwest or AOL, if they're accessing you through a university, through a government building's computer.
You usually won't be able to find out anything directly about the name and address of the person viewing your journal by their IP address. The IP addresses that people access the web through are usually owned by an internet service provider, versus a website's IP address, which will often have registry information identifying the name and possibly address of the owner.
Each ISP typically has a block of IP addresses, and behind that block of public IP addresses, there may be layers upon layers of private networks. My apartment has at least two layers of local area network between my computer and my roommate's computer and the great big wide web. If my roommate and I are both accessing LiveJournal from home, we have identical IP addresses, even though LJ knows we're different people. We have one cable modem talking to Cox, and that cable modem might get a different IP address from day to day. The IP address I had today might get assigned to someone else down the street or across town tomorrow.
If you have a bunch of regular readers, and you have taken the time to match up IP addresses on comments to IP addresses coming in from your visitor tracking service, you probably have a good idea who is who visiting your journal. Odds are that your assumption will be right, but there is always that chance that their roommate is poking at your journal today, or their neighbor stumbled across your journal. There's just enough uncertainty that LiveJournal will not generally act on IP-address-linked-to-username information.
It's relatively easy to get around tracking services that you know about, or even some that you don't personally know about. If you have a smart modern browser, you will be able to block either that image, or all images from that domain, from loading at all. If the image doesn't load, then your tracking service has no idea that the page has loaded, and won't register the visit. AdBlock is a popular extension for the popular browser FireFox, and there may well be privacy lists for it to block all known tracking images, and there must surely be other similar services that include the major visitor tracking sites and some minor ones too.
Merely having an external visitor tracking service on your journal will not deter stalkers, or even necessarily detect them. It may deter some, to be sure, but someone who is sufficiently smart about the internet may bounce by once, tell their browser to never load your tracking image again, and proceed to surf freely through your public items without leaving a trace.
Assuming your visitors are kind enough to allow the tracking image to load, or a stalker is clueless enough to leave your tracking image alone, where is the best place to put a tracking image on your journal?
I have a tracking image on my profile, and it really isn't a great place for it. LiveJournal's content is not on the profile. I only catch people surfing to me through other people's profiles, or coming to check out my interests or contact info. I get new people coming through, or people surfing in through my info from a community. There are some people who come there first week after week; if I check my tracking logs, I do see some of the same ISPs over and over. But I know most people are going to come in on my main journal page.
LiveJournal's content is on the main journal page. If I wanted to accurately track visitors to my journal, I'd put a tracking image on the main page of my journal, either in a dated-out-of-order post at the top of my journal, or somewhere in the style itself. This will catch the visitors to my journal without me having to do anything out of my way once I have it set up and tracking. Unlike MySpace, the blog is the main content on LiveJournal, not tacked on as an afterthought.
If I were trying to track visits to individual entries, I would embed a tracking image, even an individual tracking image, in each entry. But that would get me deceptive hits, phantom hits, hits that may not correspond to an actual visit to my real journal. It doesn't make sense until you think about LiveJournal's major timesink: the friends page.
Unless a tracking image in an entry is hidden behind an lj-cut, the image may get a billion hits from someone who abuses their friends page the way I do mine when I'm bored and don't have particularly anything else to do. The entry may be halfway down the friends page, and my friend may be refreshing their friends page and staring at the top, willing their favorite comic's feed to update so they can get first post. That measures how bored my friends are and what they're doing to their friends page when my post happens to be on it, not whether they're actually reading my post. If my entry is post 19 on a 20-post page and all my friend can see without scrolling down is the five posts at the top, my image tracker is still going to pick up a hit every time that page gets refreshed until the post moves off the page. I might put a tracking image in a comment on a particularly popular or controversial post, just to see if anything interesting turned up, but otherwise I do not think I would bother to track individual posts.
There is a rather overlooked page that I would put a tracking image in to check for stalking: the calendar pages! People don't tend to think of putting a tracker on the calendar pages, but if I were worried about stalkers, I would very much track those pages, to see if someone was going through them, and if it was the same person over and over.
Even though tracking visits to your LJ won't necessarily reflect the people you think it is, or catch people who are determined not to be caught while surfing through your journal, feel free to try and track visits to your journal. Just take care to do it right.